Various materials have been developed as “scaffolds” to be used for regenerative medicine. Typical examples of the materials may include synthetic polymers such as poly-glycolic acid (PGA), poly-L-lactic acid (PLLA), and poly-lactic-co-glycolic acid (PLGA) as a complex thereof; and natural polymers such as collagen and gelatin. These materials have already been used in clinical practice and have yielded definite results (Non-patent Literature 1 to 4). However, for example, use of the poly-glycolic acid in vivo may induce an inflammatory reaction due to a local reduction in pH, resulting in needless adhesion (Non-patent Literature 5). In addition, collagen has tissue compatibility but may cause a problem of insufficient durability for some organs or sites to be regenerated (Non-patent Literature 6).